The present invention relates to an antiglare device, suitable for glasses, helmets and masks.
Antiglare devices are widely used in the welding and cutting torch technology, but are also used in the military and entertainment industries. As a rule, with these antiglare devices the radiation above 780 nm (infrared) and below 365 nm (ultraviolet) are filtered and only the radiation in the visible range is dimmed.
For example, in German patent DE 2,606,416, antiglare devices with a liquid crystal cell arranged between two polarizing sheets are described. This liquid crystal exhibits a frequency-dependent anisotropy of the dielectric constant, i.e., changes its homeotropic orientation as a function of the applied frequency of the electric alternating field. The switching times that can be realized in such a manner, i.e., the dimming time, respectively brightening time, are about 50 msec.
In U.S. Pat. No. 3,575,491, an electronic circuit is described for the purpose of operating liquid crystal cells in order to reduce the switching times to as far as 0.5 msec. This circuit functions with a voltage exceeding 125V.
In these known antiglare devices the switching time is device specific, i.e., depends on the respective construction, electronic circuit and the components that are used. The currently useful antiglare devices are characterized by unusually short switching times and low output.
However, it has been demonstrated that the short switching times are absolutely necessary for the darkening phase, but are not always desired for the brightening phase. In particular, when welding hot welding materials with long after-glow time, short brightening times result in intensive glares immediately after completion of the welding process.
On the other hand, short welding times can be necessary especially for spot or tack welding, as for example, to enable the work to be done rapidly with short cycles.